Polymeric materials such as polypropylene, low density polyethylene, alpha-olefin modified polypropylene, polystyrene, poly(4-methylpentene-1) and other organic polymeric materials having substantially non-polar characteristics are used in high volume applications in the packaging industry and are usually considered to have relatively low surface energies. These materials may be in the form of injection molded parts, free extruded films, and extrusion coatings on substrates such as paper, metal foils or non-woven fabrics. It is often desirable to modify the surface properties of these materials for special purposes such as for improved wettability, printing and coating of the polymers.
Methods for increasing the surface energies of polymeric materials are described, for example, in U.S. Pat. No. 5,272,196 to Gardiner and U.S. Pat. No. 5,281,438 to Gardiner et al. The methods described in the '196 and '438 patents employ an amphiphilic resin of the formula EQU RA(CHR.sup.2 (CH.sub.2).sub.n A.sup.1).sub.m R.sub.1
wherein R and R.sup.1 are selected from the group consisting of alkyl, aryl and alkylaryl groups and acyl and arylacyl derivatives of an aliphatic or aliphatic/aromatic mono-acid with a molecular weight of from about 200 to about 500 daltons, A and A.sup.1 are selected from the group consisting of --O--, --S-- and --NR.sup.3- wherein R.sup.2 and R.sup.3 are selected from the group consisting of H, CH.sub.3 and C.sub.2 H.sub.5, n is an integer from 0 to 3 and m is an integer from 2 to 20. The resin is blended with a non-polar polymeric material to increase the surface energy of the material.
U.S. Pat. No. 4,604,425 to Ohmura et al. describes modification of the surface of a polymeric material by adding a peroxy or azo derived diblock copolymer to the polymeric material. According to the '425 patent, the diblock copolymer must have at least two peroxy bonds in the molecule in order to be effective. However, it is well known that diblock copolymers are not effective surface modification agents for polymeric materials because they tend to form micelles in the host polymeric material. The micelles inhibit the migration of the hydrophilic portions of the copolymer to the surface of the host material. Under carefully controlled laboratory conditions the hydrophilic ends of the copolymers can be made to migrate to the surface to a limited degree. However, such conditions are largely impractical for commercial applications.
It is therefore an object of the invention to provide compositions for modifying the surface properties of polymeric materials, especially non-polar polymers.
It is another object of the present invention to provide a non-polar polymer which exhibits enhanced hydrophilicity and wettability.
Another object of the invention is to provide a non-polar polymeric material exhibiting improved printability and coatability using a range of inks and coatings heretofore difficult to apply to such materials.
A further object of the invention is to provide an additive for a non-polar polymeric material which is adaptable in a range of embodiments to tailor the polymer for various end use applications.
Still another object of the invention is to provide an additive for a non-polar polymeric material which is relatively simple and inexpensive to manufacture and which is readily incorporated into the polymer materials.